1. Field of the Invention
This invention relates to an etching method of a conductive film which remarkably simplifies the etching process in comparison with the conventional photoresist and silk screen methods.
The present invention relates to a method of etching an electrically conductive film on a material consisting of a substrate and the conductive film deposited on the former, and having surface conduction in a desired pattern in accordance with a particular application.
The present invention relates further to an etching solution which is suitable for use in etching the conductive film.
2. Description of the Prior Art
Heretofore known materials having conductive film deposited on a substrate include those which have a metal film such as gold or aluminum film or a metal oxide film such as tin oxide or indium oxide on a substrate such as a glass sheet or a film. According to their construction, they naturally have surface conduction. Some of the materials having the metal or metal oxide film vacuum evaporated on the substrate are transparent and are known as nesa glass and transparent conductive films.
Because of their surface conduction, they are used for flexible circuits, antistatic applications, electromagnetic shield, touch panels, panel heaters, and so forth. Especially those materials which are transparent and electrically conductive have gained a wide application in the field of electronics such as electrodes for liquid crystal display, for light emission in the electric field, for photoelectric sensitive members and the like where transparency and electric conduction are necessary.
In the application described above, it is very seldom that the materials having the surface conduction are used as such without post-treatment. Depending upon the intended application, the conductive portion is etched in a necessary pattern, a conductive paint or a protective coating film is coated on the conductive surface and a tackifier and an adhesive are coated on the conductive surface and non-conductive surface.
To etch the conductive film formed on the substrate, it has been a customary practice to employ a method, which fundamentally forms a mask on the conductive surface, by forming first the mask on the surface of the conductive film and then carrying out etching, by a photoresist process or a screen printing process. The method which forms the mask and then makes etching in accordance with the photoresist process is used for forming electronic circuits such as ICs, while the method which first forms the mask and then makes etching in accordance with the screen printing process is used for an electrode from a copper laminate sheet or the like.
The photoresist process will be described in detail. First, a photosensitive resin layer is deposited on the conductive surface by coating or lamination. The layer is then exposed to ultraviolet light. The pattern portion is crosslinked and becomes insoluble to a solvent; hence, only the portions that are not cross-linked are dissolved and removed by the solvent and the solvent is dried to obtain the mask. Next, the conductive film is removed from the portion where the mask is not formed, by dipping the material into an etching solution or spraying the etching solution to the material, followed then by washing with water and drying. Finally, the material is dipped into a solvent which swells the mask to remove it. After the solvent is dried, etching is completed to provide the desired pattern. Thus, the photoresist process requires a large number of steps.
The silk screen process is practised in the following way. First, a silk screen is prepared to print a masking material for ink or the like in the pattern and the masking material is then printed onto the conductive surface via the silk screen, followed by drying to provide the mask. The subsequent steps are the same as those of the photoresist process and a large number of steps are also necessary. The silk screen method can produce large quantities of masks on the conductive surface within a short period of time. For this reason, this process makes a greater contribution to the reduction of etching cost than the photoresist but the etching cost itself is still high because the subsequent steps are large.